In the latter part of World War II, Germany used submarines to transport military cargo and began to design underwater cargo ships for carrying dry cargo.
More recently, research has been performed on underwater vessels using nuclear power. In particular, researchers have investigated the possibility of constructing underwater oil tankers, underwater vessels for carrying minerals and sand, and other underwater dry cargo vessels for carrying 20–50 thousand tons of cargo. Underwater vessels may be attractive in military applications and can sail under ice. Certain voyages can be shortened greatly by passing through the arctic seas. Hidden transportation can be advantageous during times of war. Nuclear-powered high speed underwater oil tankers may have certain advantages over normal oil tankers operating at comparable speeds and with comparable cargo weights during storms.
Underwater oil tankers are also attractive because their holds are full of liquid oil, which cannot be compressed. Because the internal and external pressures on the hold stay equal at various depths under water, unpressurized holds may be used. The loading of this type of vessel can be 30% greater than a vessel of the same tonnage using a pressurized hold. There is also no need to use lifting equipment when loading and unloading oil. Oil can be removed through a small hole in the vessel's hull. It is easy to create this type of small hole using modern submarine technology. To date, there are essentially no viable underwater dry cargo transportation vessels available.